by Jayne O'Donnell, USA TODAY

by Jayne O'Donnell, USA TODAY

Legally married gay couples may want to take another look at tax returns filed since their weddings.

Thanks to the Supreme Court Wednesday, these couples may be eligible to amend their returns to file jointly and take other deductions previously only available to opposite-sex spouses, at least if they live in states that recognize gay marriage.

Those couples are "golden," says Fred Sainz, vice president of communications for the Human Rights Campaign, the largest gay rights lobby. "They will be treated no differently than opposite sex couples within days."

The court upheld a ruling that legalized same-sex marriage in California and struck down the federal Defense of Marriage Act that denied federal benefits to same-sex couples already married in 12 states.

"The path is less clear" -- until the Internal Revenue Service issues guidance -- for couples who were married in a state where gay marriage is legal, but live in a state that doesn't recognize it, says Sainz, because the IRS currently uses the filer's state of residence as a guide on marriage, he says. Washington, D.C., and 13 states -- accounting for about 30% of the U.S. population -- recognize gay marriage.

Another big question, says Annette Nellen, a professor of accounting and taxation at San Jose State University, is that the Internal Revenue Code refers at least 30 times to couples as a "husband and a wife." She wonders if the IRS will clarify that or if Congress will get involved.

The Wednesday ruling could affect the tax returns of more than 100,000 couples. There are nearly 650,000 same-sex couples in the U.S., of whom about 114,100 are legally married and 76,000 live in states recognizing it, according to a February report by the Williams Institute, a think tank that studies sexual orientation and gender identity law.

Among the ways experts say taxes and benefits could change for married gay couples, at least for those who live in a state recognizing the marriage:

ā?¢ Income taxes: The Williams report found most married lesbian, gay, bisexual and transgender (LGBT) workers pay more in income taxes than they would if allowed to file as "married, filing jointly," especially for spouses with very different incomes. For example, a working parent with a taxable income of $60,000 a year and a stay-at-home spouse with no income would pay $2,900 more as individuals than filing as a couple. That might not be true for couples with higher and more equal incomes, however.

Also, until now, working LGBT parents couldn't establish legal ties to their spouses' children, so generally were not able to claim child-related exemptions, deductions and credits, including the child and dependent care expense credit, and several education-related deductions, the report said.

ā?¢Social Security: Surviving spouses would now likely be able to collect the deceased spouse's Social Security checks if that amount is higher than the one he or she was currently receiving. Under the Defense of Marriage Act, gay married couples were denied certain Social Security benefits, which could cost a retired same-sex couple up to $14,484 per year and a surviving same-sex spouse or partner up to $28,968 per year, according to a 2013 report from the Center for American Progress, the Human Rights Campaign and the Movement Advancement Project.

ā?¢Federal estate taxes: An unlimited marital deduction now applies on both the state and federal level, so all assets could pass to a surviving same-sex spouse without tax.

ā?¢Rollover of retirement plans: Individual Retirement Accounts no longer would be taxed before they are rolled over to a surviving gay spouse's account. And pensions now could be left to same-sex spouses.

One thing Nellen says she knows for sure: "States are going to have to take a look at 'what does this mean' for all of our taxes," she says.